1. Field of the Invention
The invention relates to clutches, and more particularly, to clutches which are operated automatically by centrifugal force at a predetermined speed of rotation so as to connect a driving member to a driven member or load. More particularly, the invention relates to an improved centrifugal clutch construction of the type having a pair of pivotally mounted clutch shoes which swing outwardly into coupling engagement with a driven clutch member.
2. Description of the Prior Art
There are numerous types and arrangements of centrifugal clutch constructions in which one or more clutch shoes are retained in retracted position by springs until sufficient centrifugal force acts on the shoes to overcome the force of retaining springs, whereupon the clutch shoes pivot and swing outwardly and engage a stationary clutch housing or drum.
Many of these clutch constructions have a pair of arcuate-shaped clutch shoes which are pivotally mounted on a clutch backing plate and arranged in an end-to-end relationship with respect to each other. The backing plate in turn is fixed to a drive shaft or hub for rotation with the drive shaft. These clutch shoes have various spring arrangements for biasing the shoes toward retracted position, which spring retaining tensions must be overcome by the centrifugal force before the clutch shoes engage the driven member.
Many of these types of centrifugal clutches have proven satisfactory for their intended use. Most of these known clutch constructions use a simple beam-type pivotal mounting arrangement for the clutch shoes, that is, the pivot pin is supported on both ends by a pair of backing plates or other fixed components, with the clutch shoe pivotal connection being formed between these spaced supports on the pivot pin. These simple beam-type clutch mounting constructions result in a clutch having a relatively wide configuration in an axial direction due to the clutch shoe pivot pin supports being on both sides of the pin to provide the necessary strength and rigidity thereto. This excessive width limits or prevents the clutch from being used in certain installations where space is critical.
These simple beam-type pivot pin mounting arrangements generally include a pivot pin or its equivalent which projects through an opening formed adjacent one end of each of the clutch shoes to form the pivotal connection for the shoe. Metal bearing sleeves have been provided in some of the structures to assist in the pivotal movement of the clutch shoes on the pins. These metal-to-metal pivot pin mounting arrangements transmit the coupling shock and other forces which are exerted on the clutch shoes when engaging the driven drum, directly to the pivot pin and associated pin mounting plates or components. This force transmittal, in addition to causing fatigue in the connecting components, results in a relatively rough coupling with the driven member.
Another problem or disadvantage of these prior type clutch constructions is that a somewhat different clutch must be designed and built for each particular operating condition so that the clutch shoes will engage or disengage the driven member upon the drive shaft reaching a predetermined speed. These engagement and disengagement speeds may vary due to changes in the retaining spring characteristics which can be affected by ambient temperature, age, wear, etc. It is desirable to be able to maintain the same engagement and disengagement speeds as the age of the clutch increases without replacing the biasing springs. Likewise, in many applications it is desirable to change more radically the engagement and disengagement speeds to achieve different clutch operating characteristics. The engagement and disengagement speeds, among other factors, are dependent upon the weight of the clutch shoes. Some known clutch constructions have provided means for replacing the clutch shoes with different shoes of varying weights to achieve different clutch operating characteristics. This arrangement involves considerable time and expense required to replace both clutch shoes. Another clutch construction provides a shoe having a tube for receiving varying amounts of B-B's or lead shot for changing the shoe weight, such as shown in U.S. Pat. No. 3,687,254.
U.S. Pat. No. 2,087,968 discloses a centrifugal clutch construction in which the clutch shoes are slidably, pivotally mounted on a type of cantilever anchor pin which engages a U-shaped slot formed in the end of the shoe. A second pin which is fixed to the backing plate and extends through a slotted opening in the other end of the shoe is required to provide the desired self-energizing action. This slotted end mounting arrangement may present undesirable operating characteristics in certain installations due to the repeated outward and rearward movement of the clutch shoe slotted end from the anchor pin. An undesirable shock or force is exerted on the slotted shoe end each time it strikes the anchor pin upon its return. The shoe end should be fixed with respect to its anchor post or pivot pin to prevent these undesirable forces from repeatedly being exerted on the pivot pin. U.S. Pat. No. 2,087,968 also discloses the use of weighted washers mounted on the shoes at the swinging ends of the shoes, in order to change the shoe operating characteristics. The mounting of the weights at the ends of the shoes could shift the center of gravity off-center of the shoe which could effect the operation thereof.
There is no known centrifugal clutch construction of which I am aware which provides for pivotally mounting the clutch shoes on cantilever-type pins to eliminate the heretofore space occupying, simple beam-type pivot pin mounting arrangement in which pivot pin bushing assemblies absorb much of the stresses and shocks exerted on the clutch shoes; and which provides an extremely simple and inexpensive means of changing the weight of the clutch shoes to achieve different clutch operating characteristics without unbalancing the weight distribution of the shoes.